Customized worlds (#387)

* Customized tool UI

* Working version of the customized generator

* Error reporting and only allow 1.20 for now

src/locales/en.json

@@ -31,6 +31,9 @@
   "copy_share": "Copy share link",
   "copied": "Copied!",
   "copy_context": "Copy context",
+  "customized.basic": "Basic",
+  "customized.structures": "Structures",
+  "customized.ores": "Ores",
   "cutoff": "Cutoff",
   "damage_type": "Damage type",
   "developed_by": "Developed by",
@@ -129,6 +132,7 @@
   "theme.light": "Light",
   "theme.system": "System",
   "title.changelog": "Technical Changelog",
+  "title.customized": "Customized Worlds",
   "title.generator": "%0% Generator",
   "title.generator_category": "%0% Generators",
   "title.generators": "Data Pack Generators",